Distributer cap test

Keith · Post by **Keith** » Sun Jan 17, 2010 11:23 am

I'm working on a 24v dist on my M38. I've been trouble shooting an ingnition problem for 3 weeks now and I was just testing continuity with my auto meter, on the dist cap that I just purchased from Debellas, between were the plug wire goes in and the under side were the rotor arcs to and I get OL (open line) on all 4 positions so I grab my old cap and the samething "OL"!! So i swithched to ohms and I get an average of 5.00 K ohms. I then test my old civi dist cap and its what I was expecting .30 ohms and good continuity.

Is the 24v dist cap supposed to be like that or is this what my problem has been this whole time?

Thanks
Keith

Post by **Ryan_Miller** » Mon Jan 18, 2010 2:06 pm

Hey,

I am not sure on cap continuity, but what all is going on with the ignition problem. A little more background info would help - sorry if it was posted elsewhere and I missed it.

Post by **wesk** » Mon Jan 18, 2010 6:45 pm

Just to check I measured Ohms on 3 caps I have and they all read an average of 5.0 with the best at 4.22 and the worse at almost 10.0. These are all brown US built caps. What color is your cap? Is it US made?

My rule is if the part can leave me stranded where I don't want to be left stranded then I buy American Made. With distributors you want to avoid the off shore caps and coils.

A fellow asked me once why I preferred the TurboProp Cessna twin over the Piston powered Cessna twin. It was simple arithmetic, the turbo-prop engine built by P&W has a 99% reliability rate vs 85% on the piston engine.

Just curious what the first setting you used on your tester was before you switched to the OHMs position?

Keith · Post by **Keith** » Tue Jan 19, 2010 1:29 pm

the first test was just checking continuity and it read OL for openline. I've put it back together with a laundry list of tests and replacement parts and still at square one.

After engine, electrical, and fuel system restoration 6 months ago its been running great.

original problem- after a short 4 mile drive it wouldn't ideal, i had to keep the rpms up to keep it running and more than normal black smoke at lower rpms

in order as I tested, checked, and replaced

1 checked carb float level, needle valve, etc, everything clean and GOOD

2 fuel pump pressure 3.5-4 psi GOOD

3 timming, it made no change

4 tested compression #1 65psi, #2 110psi, #3 110psi, #4 110psi, put a couple squirts of oil in #1 cyl and rechecked Now its at 90psi

5 checked points and gap no change

6 Now it won't start at all

7 replaced one at a time coil, then condenser, then capasitor, then the cap no change

8 repeated 7 AGAIN no change

9 pulled it untill it started and its running worse than ever and now its only running on 2 cylinders, 2&3 firing 1&4 are cool to the touch on the exhaust manafold

10 replaced cam shaft timing gear no change

11 removed oil pump and checked the roll pin on the gear no problem there

12 reset all tming according to TM 9-1804A still only 2 cyl firing

13 replaced all 4 plugs with new autolite 2243

14 NOW all 4 cyl are firing BUT its back running like the original problem.

15 getting someone elses opionion, is just because of low compression on #1

All my replacment parts hve been from midwest or Debellas

Thanks for everyones input,
Keith

Post by **wesk** » Tue Jan 19, 2010 8:03 pm

Have you done a pressure leakdown test yet?

Keith · Post by **Keith** » Wed Jan 20, 2010 12:42 pm

No I have not performed a pressure leakdown test and I'm not sure what it is.

last night I had someone with more experience than me take a fresh look at it and we found a small crack in the intake manifold near the #1&2 port. he also noticed the bottom portion of the carb was sweating. he sprayed some wd-40 on the crack and and it changed the idle a little.

any other advise or thoughts always appreciated.

I hope replacing the intake manifold will solve the problem.

Thanks
Keith

Post by **wesk** » Wed Jan 20, 2010 2:17 pm

With the manifold leak that would explain a burned valve or seat which in turn would explain the low compression in #1.

A leak down test is used to determine exactly where the compression pressure is leaking off to. You pressurize the cylinder to about 80 PSI and if the air escaping noise is in the carb you have an intake valve leaking. If the noise is in the tail pipe you have an exhaust valve leak. If the noise comes from the dipstick tube it's leaking past the rings and if bubbles come up in the coolant at the top of the radiator you have a head gasket leak or cracked cylinder. I have used this test for 50 years and it does not lie and it quickly narrows down the suspect when a standard compression check indicates a low cylinder.

Keith · Post by **Keith** » Thu Jan 21, 2010 9:07 am

I did the leakdown test and its the rings. I also put some hi temp silicone on the the small intake manifold crack and no change.

thanks
Keith